Cable trays are, in general, support structures used in commercial and other buildings and in connection with other structures to support or otherwise carry long runs of electrical wiring, conduit and the like relative to the buildings or other structures. A typical cable tray comprises a pair of parallel elongate rails connected by a plurality of cross members spaced apart along the length of the parallel rails. The long runs of electrical wiring, conduit and the like are laid into the cable tray along the length of the parallel rails and transverse the plurality of spaced apart cross members.
The cable trays themselves are, in general, supported relative to fixed structures and commercial or other buildings by a series of parallel support bars suspended at intervals and spaced lengthwise of the cable tray. The cable tray rests on these support bars and is held in position on the bars by hold-down members which are affixed to the support bars by suitable fasteners such as threaded bolts and captive nuts or the like. These hold-down members are intended to hold the cable tray on the support bars and to prevent lateral shifting of the cable tray relative to the support bars.
One type of hold-down member prevalent in the industry is functional to rigidly clamp a cable tray against its support. These are commonly referred to as fixed clamps. Another common type of hold-down member holds the cable tray loosely on the support bars to permit selective relative movement between the cable tray and support bars necessitated largely by thermal expansion and contraction of the cable tray due to temperature variations. These are commonly referred to as expansion clamps. Accordingly, in practice, in order to permit relative movement between the cable tray and the support bars in selected regions along the length of the cable tray, several expansion clamps are used in the selected regions between pairs of fixed clamps on the ends of the regions. In some applications, as many as dozens of expansion clamps may be used in the selected expansion regions between pairs of fixed clamps. It is to be appreciated that a run of a cable tray system may span several expansion regions along its length.
For many reasons including economy, ease of use, and a reduced parts list, it is preferable to have a single “combination” hold-down member which is selectively functional in both capacities. Combination hold-down members can be selectively applied in either a clamping (fixed) mode or non-clamping (expansion) mode.
It is extremely important, however, to correctly install these combination hold-down members in the clamping mode when it is desired to fixedly clamp the cable tray to the support bar(s) and, correspondingly, to install the combination hold-down members in the non-clamping mode when it is desired to loosely clamp the cable tray to the support bar(s). Misapplication of the hold-down members could adversely interfere with providing for the required relative movement between the cable tray and the support bars in the selected designated regions wherein a failure of the connections, a buckling of the cable tray or the like could occur as the cable tray expands, contracts, and vibrates relative to the support.
Some applications do not lend themselves to close post-installation inspection such as for example high overhead uses. Accordingly, it is difficult to visually verify that the hold-down members are properly installed in the prescribed modalities along the length of the cable tray.